Compressor

ABSTRACT

In the case of a compressed air compressor, intake openings located in the cylinder covers are connected to intake pipes made from elastomeric material, the length of which pipes amounts to a multiple of the clear cross-section. The intake pipes have a semicircular pipe portion at the cylinder end and a straight free pipe portion, which extends over the outer surface of the associated cylinder at a slight distance therefrom.

The invention relates to a compressor according to the precharacterising clause of claim 1.

Such a compressor is disclosed in EP 0 335 362 B1. It is distinguished by compact dimensions together with good delivery characteristics and quiet running.

For many applications it would be desirable for such a compressor to create even less noise while running.

To achieve this object the present invention proposes a compressor with the features stated in claim 1.

In the case of the compressor according to the invention, the intake openings of the various cylinders are each provided with an intake pipe, the length of which is long compared with the clear cross-section of the intake pipe. In this way, the intake noise is considerably reduced.

Surprisingly, the volumetric flow rate (the delivery capacity) is additionally increased by approx. 5%. The reduction in overall noise level achieved by the intake pipe amounts at average audio frequencies of from approx. 100 Hz to 2 kHz to approx. 3 to 9 dB(A).

Advantageous further developments of the invention are indicated in the dependent claims.

Claim 2 states preferred ratios between the length of the intake pipes and the clear internal diameter thereof.

The further development of the invention according to claim 3 is advantageous with regard to simple attachment of the intake pipes to the cylinders.

Claim 4 provides a simple detachable connection between intake pipes and cylinders.

In the case of the compressor according to claim 5, the intake filters may also contribute to sound absorption.

A compressor as indicated in claim 6 has particularly favourable flow conditions at the ends of the intake pipes, which likewise has a favourable effect on noise development.

Claim 7 states particularly well-proven curvature conditions for the end of the intake channel provided in the intake pipes.

The further development of the invention according to claim 8 is also advantageous with regard to favourable flow conditions at the inlet of the intake pipes.

The diameters of the intake channel, as stated in claim 9, have proven particularly advantageous for compressors of moderate delivery capacity (40 to 250 l/min), as are often used in dental practices.

The further development of the invention according to claim 10 makes it possible to position a longer major part of the intake pipe at a point at which free space is still available within the clear contour in the case of the compressor considered in each case.

In the case of a compressor according to claim 11, the longer straight pipe portion may extend parallel to an outer surface of the cylinders, if the cylinder-side end of the intake pipe is connected to an air intake opening, which, as is often conventional, is provided in the cover of the cylinder.

The further development of the invention according to claim 12 is advantageous with regard to good sound absorption in the case of intake pipe dimensions which enlarge the clear contour of the compressor only slightly.

The further development of the invention according to claim 13 is advantageous with respect on the one hand to achieving maximum sound absorption and on the other hand also to ensuring unthrottled access by the air to the inlet of the intake pipes.

The further development of the invention according to claims 14 and 15 is advantageous with regard to further improvement of sound absorption.

The further development of the invention according to claim 16 is advantageous with regard to further improved sound absorption.

A compressor according to claim 17 is of particularly compact construction. Furthermore, the intake areas of both cylinder units are spatially separated.

In the case of a compressor according to claim 18, relatively cool air flows into the inlet ends of the intake pipes, which contributes to better cylinder filling.

The invention is explained in greater detail below by means of exemplary embodiments with reference to drawings, in which:

FIG. 1: is a perspective view of a two-cylinder compressor with the cylinders in a V arrangement, the cylinder located on the left in the drawings and an intake pipe thereof being shown partially in section;

FIG. 2: is a plan view of the compressor according to FIG. 1, from the left thereof;

FIG. 3: is an axial section through an intake pipe of the compressor according to FIGS. 1 and 2 on an enlarged scale;

FIG. 4: is a plan view of the intake pipe in FIG. 3 viewed from above; and

FIG. 5: is a graph showing the effect of noise-reducing intake pipes in a two-cylinder compressor with a delivery capacity typical of dental applications.

The two-cylinder compressor in V arrangement shown in the Figures has a drive unit designated overall as 10, which comprises an electric motor 12 and a crank drive unit 14. The crank drive unit 14 has a housing 16, into which the shaft of the electric motor 12 is drawn. The latter there bears two angularly offset crank pins, which drive pistons via connecting rods, likewise not shown.

Details of the internal structure of the drive unit 14 are revealed by the above-mentioned EP 0 335 3 62 B1, to which reference is explicitly made in this respect.

The housing 16 of the crank drive unit 14 is closed at the front by a grille 18, behind which there is located a fan impeller 20 driven by the motor shaft. The latter serves to draw in cooling air for the drive unit 14 and the electric 10 motor 12.

The housing 16 of the drive unit 14 displays a substantially square, prismatic geometry, and a compression unit 22 is positioned on each of two of its outer faces.

Each of the compression units 22 comprises a cylinder block 24, a cylinder cover 26 closing the radially outer end thereof and the piston, not shown in the drawings, extending inside the cylinder block 24.

An inlet valve and an outlet valve are accommodated in the cylinder cover 26, as is clear in detail from EP 0 335 362 B1.

The inlet valve of the compression units 22 is connected in each case with a filter chamber 28, which is constructed so as to extend parallel to the cylinder axis at one of the corners of the cylinder block 24.

The outer end of the filter chamber 28 is closed by a fitting 30, which comprises a central through channel 32. A filter cartridge 34 is positioned on the bottom of the fitting 30, which cartridge retains impurities in the air which has been drawn in and may be replaced after removal of the fitting 30.

At its free, upper end, the fitting 30 has a radial mounting flange 36, which may cooperate in latching manner with a latching groove 38, which is provided at the cylinder-side end of an intake pipe designated overall as 40.

The intake pipe is similar in design to a walking stick and comprises a bent pipe portion 42 at the cylinder end and a straight pipe portion 44 borne thereby.

As is clear from the drawings, the bent pipe portion 42 extends over a circumferential angle of 180°. Its diameter is selected in such a way that the straight pipe portion 44 extends over the outer surface of the cylinder block 24 at a slight distance therefrom. The pipe portions 42 and 44 together form a correspondingly curved intake channel 46, which leads back from the upper end of the cylinder block 24 to the outer surface of the housing 16.

At the free end the intake pipe 40 is provided with a toroidal bead 48, which, when viewed in axial section, extends over a circumferential angle of approx. 270°. It provides a smooth connection between the outer surface of the intake pipe 40 and the end of the intake channel 46.

In a practical exemplary embodiment of such an intake pipe 40, as used in compressors with a delivery capacity of approx. 120 l/min and a connected load of the electric motor 12 of approx. 1.5 kW, the length of the pipe portion 44 is approx. 110 mm, the radius of the centre line of the pipe portion 42 is approx. 16 mm, the clear diameter of the intake channel 46 is approx. 8 mm and the wall thickness of the intake pipe 40 is approx. 4 mm at the free end and 6 mm at the cylinder-side end.

As is apparent from the drawings, the straight pipe portion 44 of the intake pipe 40 extends over somewhat more than 90% of the axial extent of the cylinder unit formed by cylinder block 24 and cylinder cover 26. In this way the compressor draws in air from the vicinity of the cool outer surface of the housing 16, the flow cross-section remaining large enough, however, to ensure that no appreciable throttling of the drawn-in air takes place between the end face of the intake pipe 40 and the outer surface of the housing 16.

A material which is generally suitable for the intake pipe 40 is an elastomeric material, in particular a silicone material, with a Shore A hardness of 50 to 70, preferably approx. 60.

If it is important to achieve a very great reduction in noise level, it is possible (in particular if the material of the intake pipe is relatively hard) additionally to line the inner surface of the intake pipe 40 with a sound-absorbent plastics layer 50, indicated at just one place by a broken line, and to provide noise-reducing padding 52 (e.g. foam material or knitted spring steel fabric) on the outside of the housing 16 under the free ends of the intake pipes 40, as is likewise indicated by a broken line.

The resultant overall noise reduction is then based on the one hand on the sound absorption inside the filter cartridge 34, on the sound absorption in the curved pipe portion 42, where the sound waves impinge on the wall material of the intake pipe 40 and are reflected thereby, on the sound absorption in the straight pipe portion 44, where the sound waves are repeatedly reflected until they reach the free end of the intake pipe 40, and on the sound absorption by impingement on the outside of the housing 16. Sound may be further absorbed by the plastics layer 50 and the padding 52, if these measures are provided.

It is apparent from the above description that the described compressor provides additional noise reduction without the clear contour of the compressor being increased appreciably relative to a conventional compressor.

In the case of a two-cylinder compressor for dental purposes, the magnitude of this effect is that illustrated as a function of frequency in FIG. 5. 

1. A compressor having at least one compression unit, which comprises a cylinder and a piston extending therein, and having a drive motor acting on the compression units, the cylinder in each case comprising an intake opening for decompressed gas and an intake opening for compressed gas, wherein at least one of the intake openings is connected to a bent intake pipe, the length of which amounts to a multiple of the clear diameter of the intake pipe.
 2. The compressor of claim 1, wherein the length of the intake pipe amounts to 10 to 30 times the clear diameter.
 3. The compressor of claim 1, wherein a cylinder-side end of the intake pipe is provided with coupling means, which cooperate with mating coupling means of the cylinder.
 4. The compressor of claim 3, wherein the coupling means is latching means which cooperate with the mating latching means of the cylinder.
 5. The compressor of claim 3, wherein the mating coupling means are located at the inlet of a filter chamber, in which an air filter is accommodated.
 6. The compressor of claim 1, wherein the free end of the intake pipe remote from the cylinder comprises a rounded portion, via which the end face of the intake pipe is connected smoothly with the intake channel extending in the intake pipe.
 7. The compressor of claim 6, wherein a radius of the rounded portion amounts to approximately 0.2 to 0.7 times the radius of the intake channel.
 8. The compressor of claim 7, wherein the free end of the intake pipe remote from the cylinder takes the form of a toroidal bead extending over an angle of approximately 270°.
 9. The compressor of claim 7, wherein the radius of the intake channel ranges from approximately 3 to approximately 8 mm.
 10. The compressor of claim 1, wherein the intake pipe comprises a bent pipe portion on the cylinder side and a substantially straight pipe portion borne thereby.
 11. The compressor of claim 10, wherein the bent pipe portion extends over an angle of approximately 180°.
 12. The compressor of claim 11, wherein the straight pipe portion extends over approx. 80 to 95% of the height of the cylinder.
 13. The compressor of claim 12, wherein the free end of the intake pipes ends at a distance above the outer surface of a crankcase, in which crank drives acting on the piston are accommodated, which are moved by the drive motor.
 14. The compressor of claim 13, wherein the outer surface of the crankcase is sound-absorbent at least in areas adjacent the ends of the intake pipes.
 15. The compressor of claim 1, wherein the inner surface of the intake pipes is at least partially sound-absorbent.
 16. The compressor of claim 1, wherein the intake pipes are made from an elastomeric material, which exhibits a Shore A hardness of from 50 to
 70. 17. The compressor of claim 1, including two compression units driven by a common drive motor, wherein the intake openings of the two cylinders are staggered relative to one another in the axial direction of the shaft of the drive motor, preferably being located at corners of the cylinders having square edge contours.
 18. The compressor of claim 1, wherein the ends of the intake pipes end at points where cool air is present.
 19. The compressor of claim 18, wherein the ends of the intake pipes end at a casing portion that is cooled by cooling air. 